1. Field of the Invention
The present invention relates to the epoxidation of olefins such as propylene by reaction with an organic hydroperoxide using solid epoxidation catalyst and especially to a process wherein feed to the epoxidation has been treated with aqueous base, the improvement which comprises subjecting the epoxidation feed to a treatment prior to contact with the solid epoxidation catalyst to trap and remove insoluble materials which otherwise would adversely affect the epoxidation catalyst and reaction.
2. Description of the Prior Art
It is well known to form oxirane compounds such as propylene oxide by catalytic reaction of an olefin such as propylene with an organic hydroperoxide such as ethylbenzene hydroperoxide. The basic patent describing this technology is U.S. Pat. No. 3,351,635.
In one variant of the technology an insoluble solid heterogeneous catalyst is used to catalyze the epoxidation reaction. See, for example, U.S. Pat. No. 4,367,342. A patent illustrating procedures for carrying out this reaction is U.S. Pat. No. 5,849,937.
The organic hydroperoxide, e.g. ethylbenzene hydroperoxide, is advantageously formed by molecular oxygen oxidation of ethylbenzene. See, for example, U.S. Pat. No. 4,066,706.
It is advantageous, generally, to treat process streams such as the oxidate from the hydroperoxide forming step with basic materials in order to remove acidic components which otherwise would adversely affect the epoxidation. U.S. Pat. No. 5,883,268 is illustrative. The treated streams are usually washed thereafter in order to remove basic sodium materials.
A problem which arises, however, is that if the wash normally used to remove the sodium materials fails or if there is significant entrainment of sodium materials such as during a plant upset, these materials will enter the epoxidation reactor and plug and deactivate the catalyst bed. The problem is especially acute after the oxidate has been admixed with the olefin to be epoxidized. The solubility of resinous sodium containing materials is substantially lowered when the oxidate is mixed with olefin and the resulting insoluble resinous materials are prone to plug and deactivate the epoxidation catalyst bed unless first removed.
The present invention provides protection against such catalyst bed plugging and deactivation.
In accordance with the present invention, the hydroperoxide and olefin feed admixture to the epoxidation reaction zone, wherein is contained solid epoxidation catalyst, is pretreated by passage through a screen or frit, or by passage through a bed of solid particles. As a result of this pretreatment, insoluble sodium containing resinous materials are trapped and separated from the epoxidation feed before the feed enters the epoxidation zone. Periodically, the screen or bed can be regenerated as by washing, or replaced.